Supported metal catalysts are known, and their use in numerous reactions, including the hydrogenation of fatty materials, has been described extensively in the literature. Supported nickel catalysts have been utilized in various hydrogenation processes where low IV (iodine value) fatty products are desired. A low IV is obtained when the product is completely or essentially completely saturated.
Fatty acid hydrogenations can be accomplished either in a slurry phase with a powdered catalyst or in a fixed bed with a formed catalyst. The normal catalyst of choice is based on reduced nickel as the catalytic species. However, nickel, and especially any nickel oxide, nickel hydroxide, or nickel carbonate present in the catalyst tends to react with the fatty acids to form nickel soaps. These soaps can redeposit on the catalyst or can be removed from the catalyst and accumulate in the slurry phase or can be carried off in the fatty acid liquid in a fixed bed reaction. As the amount of soap deposited on the catalyst increases, the activity of the catalyst decreases. In addition, any dissolved nickel soaps which are carried into the product can be deleterious to the quality of the reduced product.
The term "supported nickel catalyst" can be defined as a catalyst wherein the nickel precursor is deposited on a refractory metal oxide support by means of impregnation or precipitation to distribute the nickel metal as small crystallites upon the support. Examples of patents describing various nickel-containing supported catalysts and their use in catalytic hydrogenation reactions include U.S. Pat. Nos. 2,812,342 and 3,691,100. U.S. Pat. No. 2,812,342 discloses the hydrogenation of strutrurally modified acids using conventional catalysts such as Raney nickel catalysts and hydrogen. U.S. Pat. No. 4,317,748 describes a process for the preparation of supported nickel catalysts which are useful as hydrogenation catalysts, particularly for the hydrogenation of fatty materials. Examples of support materials include alumina, silica, silica gel, fumed silica, naturally occurring clays such as montmorillonite and montmofillonite-rich minerals, carbon black, activated charcoal, etc. The catalysts described in the '748 patent are typically free-flowing powders containing 25% to 75% nickel. In particular, the supported nickel catalysts are prepared by a process involving contacting a solid support material and nickel soap of a monocarboxylic acid in an inert hydrocarbon until the nickel is associated with the support. The nickel-bearing support material is then subjected to a sulfiding step followed by precipitation of nickel metal thereon. The use of an inert hydrocarbon is an essential feature of the process.
U.S. Pat. Nos. 4,174,302 and 4,317,748 describe catalysts which contain nickel and support materials which include clay. In particular, U.S. Pat. No. 4,174,302 describes a catalyst for producing cycloalkylaromatics from aromatic hydrocarbons in the presence of hydrogen wherein the catalyst consists essentially of ruthenium, nickel and a support material selected from the group consisting of active clay and silica-alumina. The catalyst contains from about 0.01 to 0.3 weight percent of ruthenium and from about 0.03 to 1 weight percent nickel. U.S. Pat. No. 4,317,748 is described above, and U.S. Pat. No. 4,584,140 describes a process for separating fatty materials from spent supported nickel catalyst composition which may also contain non-nickel-containing clays/earths.
The preparation of nickel catalysts supported on natural silicates is described by M. T. Rodrigo et at in "Applied Catalysis A: General", 88; 1992 (101-114), Elsevier Science Publishers B.V., Amsterdam. Four Spanish silicates are described as useful supports:seprolite, palygorskite, bentonite and diatomite. The powdered catalysts described in this article were prepared containing from 8.4 to 12% nickel. The activity of the catalysts was found to be almost independent of the nature of the support, whereas differences in selectivity were ascribed to differences in the morphology of the support.